Ir Filter 20f5o

FOG HORN

Gear Review

IR Filters By: Sal Palma

I continue my IR illumination series with yet another option for those seeking Infrared Illumination, the IR Filter. A filter attaches to the bezel of a handheld light or weapon mounted light and fills two important roles. Primarily, they offer you the desired output; that is red, blue, green, or in this case an IR light source to, complement your NODS. Then, a filter offers a level of protection by acting as a barrier, standing between the elements and your light’s lens. There are a couple of approaches to manufacturing filters. High quality filters are generally made by sandwiching a polymer film, of the desired characteristics, between two or more layers of glass. The less expensive approach is to use a photo film doped to produce the desired output – red, green, blue or IR.

2 October, 2010

byproducts, usually in the 1mm, more appropriately expressed as 1000nm, wavelength range. Filters used with handheld lights function to block longer wavelengths, meaning that they function to block visible light components. No filter is perfect and some leakage will occur; however, the degree to which visible light is attenuated is significant, and it is unlikely that an adversary lacking night vision capabilities will detect your approach. However, speaking as an individual with extensive ELINT experience, I want to assure you that anything transmitted can be detected, so use active devices judiciously and only when needed.

The Cadillac of the filter scene is Surefire. They produce a variety of filters in all parts of the light spectrum and in all sizes.

Light visible or invisible is part of the electromagnetic spectrum. Therefore, what can be generalized about radio frequencies may also be said about light.

The actual filter element is hinged and when IR illumination is no longer needed, the filter element is simply flipped open.

Copyright, Sal Palma dba Twobirds-Flying Publication, 2010. All rights reserved.

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The same holds true for a visible light source such as a xenon lamp or LED. The output from these point sources include near infrared

The first thing to note in the Surefire filter is the attachment method. It uses a clamping mount that makes installation quick and simple. Pulling down on the latch locks the filter in place and eliminating the possibility of it slipping off the bezel.

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For example, when we beat two radio frequencies together, as in the case of an oscillator, the output will always be the two original frequencies, the sum of both frequencies, the difference between the two frequencies and harmonics. We then employ filters on the output side of that oscillator to reject the unwanted product.

FOG HORN

Gear Review

2 October, 2010

Models include:     

FM53 FM33 FM63 FM13 FM23

1.00” bezel 1.25” bezel 1.47” bezel 1.62” bezel 2.50” bezel

All of these filters offer superb quality of construction on function to deliver an excellent source of IR illumination in the 1000nm range. They carry Cadillac prices beginning at $96 up to $176. Surefire also makes the F03 that can be used with a 1” bezel and sells for $66. The F03 simply slips over the bezel of an E2D or any other light with a one-inch bezel. Streamlight, another outstanding manufacturer of high performance tactical lights, offers a variety of filters at lower price spectrum, designed for use with their excellent line of weapon-mounted lights. The Streamlight filters can be used with the TLR-1, TLR-2 and TLR-VIR weapon mounted lights. The IR filter simply slips over the bezel and operates at the 1000nm range. Readers wishing to add an IR filter to their TLR light should purchase #69118. Streamlight filters can be purchased for as low as $16 from a number of online sources.

Photo Courtesy of Sal Palma

Conclusion While IR filters will address all but the most demanding applications, you will get superior performance from an IR LED dedicated light source.

Copyright, Sal Palma dba Twobirds-Flying Publication, 2010. All rights reserved.

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-SP

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However, don’t exclude filters from consideration because they do offer a benefit, and in most cases offer a lower cost alternative to your IR illumination needs.